Filter structures formed from thermoplastic fibers and having a functional particulate matter incorporated therein may be used for a variety of purposes. Such filter structures containing activated carbon have been used to adsorb noxious or harmful gases. Other activated particulates may be used depending on the function of the filter. For example, a biocide may be incorporated into a thermoplastic filter structure for the destruction of microbes passing through the filter. The variety of particulate matter and the functions associated therewith are extensively documented and are too extensive to list individually herein.
Examples of activated carbon filters for gas masks are disclosed in U.S. Pat. Nos. 4,981,501 and 4,992,084. These patents disclose a three dimensional carrier framework for activated carbon particles having a diameter from 0.1 to 1 mm. The carrier framework is said to be composed of wires, monofilaments or stays, the distance between the components being at least twice as great as the diameter of the adsorbent particles. A large pore reticulated polyurethane foam is specifically disclosed as a carrier framework for granular adsorbent particles. These patents also disclose that the adsorbent particles can be affixed to heterofilic fibers having two coaxially arranged components wherein one component has a lower melting point than the other. However, no method for preparing a dimensionally stable carrier framework from such heterofilic fibers is disclosed.
It would be desirable to provide a dimensionally stable filter structure from thermoplastic fibers and an active particulate matter in which the carrier framework for the structure also carries a fibrous filter material in addition to the particulate filter material. Such a filter structure could provide greater surface area for attachment of particulate matter.